Corrosive protective materials are known. Focusing on a particular field of application, prevention of corrosion is needed for steel pipelines which deliver a flowing fluid over great distances. It is not reasonably possible to permanently coat the interior of pipelines to thereby prevent rust or other products of corrosion from forming on the inside exposed wall. Most large diameter pipe is formed of ferrous materials. They are externally coated with various materials, an example being tar to protect the exterior. On the inside, however, corrosion does occur. Corrosion inhibitors are added to the flowing materials to reduce corrosion on the interior steel pipe wall.
The mix of materials flowing in the pipeline significantly changes the inhibition requirements. For example, oil field gathering lines are required to deliver the production flowing from a well. That production mix can give rise to serious problems. Varied paraffin and corrosive deposits may accumulate. Oxidation is reduced if the well produces only hydrocarbon products. However, most producing wells produce at least some portion of water along with natural gas mixed in the oil. Sometimes, the pressure drop from formation pressure to the pressure maintained in the pipeline enables lighter molecules to separate into phases, thereby flowing a mix of bubbles in liquid. The entrained gases typically will include CO.sub.2 and other gases common to a given producing formation.
All the foregoing often occurs also in the presence of produced sand. Producing formations are typically consolidated sand formations. Sometimes the sands are not well consolidated so that various and sundry sand particles are produced. These vary in size, sharpness and concentration. It is not uncommon for a producing formation to deliver sand particles which are carried along with the flow. Sand particles in the produced multiphase flow from an oil field abrasively polish the pipe surface, thereby damaging any corrosion inhibitor coating on the pipe.
Corrosion inhibitors placed in the flowing stream must have some affinity for the metal pipe. While the bond between the inhibitor and the pipe may vary, the mixed phase flow (with little, or a lot of sand) has a scrubbing or scouring impact which ranges from trivial to severe. In this disclosure, a corrosion inhibitor is set forth which can be used with most mixed phase flows in the oil field production stream. The flowing stream can readily destroy any surface pipe. Thereafter, the exposed steel pipe will corrode rapidly and form an excess of unwanted corrosion products. Accordingly, corrosion inhibition involves the formation of a first bond between the exposed steel pipe surface and the inhibitor, and then a second bond between the inhibitor and the attacking molecules in the stream. In the latter event, they will be denoted simply as corrosive agents which are characterized by available oxygen, i.e., the ultimate corrosive agent. The two bonds are noted in the discussion found below.
It has been known heretofore that the first bond is accomplished by a class of amine derived products to be described in greater detail below. The modified amines have a high affinity for the ferrous surface so that the first bond necessary to obtain protection is readily accomplished. Moreover, the amines of this class are characterized in that they have an available --N site for bonding. While it is valuable to make a bond at the --N site on the amine molecule or complex, that is not always easily accomplished because nitrogen does not readily accept chemical bonds. The reluctance of this bond is well documented in that it requires greater energy levels to accomplish. The --N bond has to be converted so that the antioxidant connected at that site provides the requisite protection against the available oxidants flowing in the stream.
This kind of bond can be obtained from phosphates, to pick an example which is detailed in Applicant's Pat. Nos. 5,611,991 and 5,661,992. In brief summary, these are directed to corrosion inhibitors which are characterized as phosphate esters. That is a highly successful inhibitor featuring phosphate as the antioxidant agent in the content of the corrosion inhibitor successfully applied in ferrous pipelines. The present disclosure, however, sets forth a much more desirable sulfur based corrosion inhibitor having significant advantages. One important advantage is the relative cost. In general terms, the cost of the inhibitor of the present disclosure is approximated by three major factors which are the cost of the amine complex, the cost of the antioxidant agent added to it and the utilities cost involved in making the corrosion inhibitor.
This disclosure sets forth a sulfur based corrosion inhibitor which is significantly less costly. Cost is reduced because the sulfur added is provided in a form that is quite inexpensive, the preferred being sulfur dioxide (SO.sub.2). Better than that, the utilities involved in plant operation for sulfur conversion are reduced significantly. As an important aspect of utility cost, sulfur products are easier and safer to manufacture in that they tend to be only slightly noxious and are generally not poisonous at the prevailing process conditions including conversion pressures and temperatures.
One aspect of this process is the synthesis of an amine which is easily bonded to the exposed ferrous surface in the pipeline along with a --N bond site available which bond is converted into an S--N bond thereby enabling the defeat of available oxygen bonds which would otherwise trigger corrosion of the ferrous surface exposed in the pipeline. Therefore, corrosion is resisted and the life of the equipment is extended significantly. This is effective at a reduced cost and yet appears to have a desirable, perhaps an even better bond to the ferrous surface. It can be used in benign conditions but it can also be used with the most aggressive circumstances, i.e., flowing multiple phase well fluids with sand particles of all sizes and shapes.
The present disclosure sets forth the improved corrosion inhibitor featuring a sulfur based active agent. The sulfur bonded amine of the present disclosure is less costly; it is also less costly to make and is made in more desirable circumstances.
The procedure of making the present disclosure involves the preparation in a first step of a specified amine structure, and the subsequent addition of sulfur in the form of SO.sub.2 that is sparged through the solution at temperatures of up to about 150-190.degree. F. at a slow rate to obtain batch conversion in a time of about 90 to 120 minutes whereupon the sulfur based inhibitor is delivered in a water soluble solution ready to be used. The conversion process is relatively simple and has reduced utility cost as a result of the shorter intervals and lower temperatures.